The use of a membrane in conjunction with air under pressure to generate sound is widely known and horns of this type can be used as ship's horns and sirens in factories. They generally are somewhat massive. Hungarian patents 89,973, 95,819, 98,353, 100,289 and 101,300 all disclose horns of this type utilizing prestressed metal sheets as the membranes and having a pair of tubes against which the membrane lies.
In U.S. Pat. No. 4,970,983, a horn is mounted on a pressurized fluid container and has a membrane of stainless steel against which a spring can bear. This membrane is received in a chamber and extends from the end of an inner tube to an outer housing member with a slight incline to the axis.
A signal device using a similar pressure source is found in U.S. Pat. No. 1,679,011 with a planar membrane or diaphragm. Similar structures are found in U.S. Pat. Nos. 870,074 and 2,918,895.
In my earlier application, the membrane, although not a metal membrane, is planar as well.